Properties of Covalent Bond
Bond Length:
Internuclear
distance between two atoms in a molecule.
Bond length
in covalent compound (AB) = rA + rB
FACTORS AFFECTING BOND LENGTH
I. Atomic
size:
Bond length α Atomic size
HF < HCl
< HBr < HI: Bond length
F2
< Cl2 < Br2 < I2
2. The
lengths of double bonds are less than the lengths of single bonds between the
same two atoms, and triple bonds are even shorter than double bonds.
Single bond > Double bond >
Triple bond
(Decreasing bond length)
3. Bond
length decreases with increase in s-character since s-orbital is smaller than a
p – orbital.
sp3
C – H = 1.112 Ã… sp2 C – H = 1.103 Ã… sp C
– H = 1.08 Ã…
Bond energy or bond strength:
Bond energy
or bond strength is defined as the amount of energy required to break a bond in
molecule.
Important
features of bond energy:
· The magnitude of the bond energy
depends on the type of bonding. Most of the covalent bonds have energy between
50 to 100 kcal mol–1 (200-400 kJ mol–1). Strength of sigma bond is more than
that of a π-bond.
· A double bond in a diatomic molecules
has a higher bond energy than a single bond and a triple bond has a higher bond
energy than a double bond between the same atoms. C ≡ C > C = C > C – C
(decreasing bond length)
· The magnitude of the bond energy
depends on the size of the atoms forming the bond, i.e. bond length. Shorter the bond length, higher is the bond
energy.
· Bond energy decreases down the group
in case of similar molecules.
· Bond energy increase in the following
order:
s < p < sp < sp2
< sp3
C – C > N – N > O – O
(No lone
pair) (One lone pair) (Two lone pair)
Bond Angles
Angle
between two adjacent bonds at an atom in a molecule made up of three or more
atoms is known as the bond angle.
Bond angles
mainly depend on the following three factors:
(i)
Hybridization: Bond
angle depends on the state of hybridization of the central atom
Generally as
the s- character increase in the hybrid bond, the bond angle also increases.
Hybridization Bond Angle
SP 180o
SP2 120o
SP3 109.5
o
(ii)
Lone pair repulsion: Bond
angle is affected by the presence of lone pair of electrons at the central
atom. A lone pair of electrons at the central atom always tries to repel the
shared pair (bonded pair) of electrons. Due to this, the bonds are displaced
slightly inside resulting in a decrease of bond angle.
(iii)
Electronegativity: If
the electronegativity of the central atom decreases, bond angle decreases.